10 of the World's Most Expensive Megaprojects
From the Top Down: Ending Sexual Harassment in the Construction Industry
Spending Up for the Month, Down for the Year
Friday Funny: "Raising the Roof"
Tracking Technology Helps Construction Companies Save Money, Improve Safety
What The ‘Tech’ Just Happened to Meetings?
Weekly Grind: The Future of Construction Technology Across the Country
Friday Funny: It's Just Ergonomics
By Jeff Wing
July 17, 2016
Teflon. Super Glue. Silly Putty. The Microwave oven. Brilliant if accidental discoveries define much of our modern world. To that odd list you can add Concrete Air Entrainment––modern construction’s best friend. As any concrete enthusiast knows, Air Entrainment is the process by which extremely tiny, uniformly distributed bubbles are deliberately introduced into liquid concrete. Why is this done, exactly?
Fluctuations in temperature are the natural enemy of concrete magnates everywhere, particularly in colder climes. In places where air temperatures can seasonally swing from hot to cold, the “freeze-thaw” phenomenon wreaks havoc on concrete. How can a little weather wreck a slab of concrete?
You wouldn’t guess this in the moments after dropping a heavy chunk of concrete onto your bare toe, but in fact, concrete is extremely porous, and it drinks in moisture like an inefficient but determined sponge. In time, all that moisture becomes trapped in the natural fissures formed inside concrete as it hardens. When the weather outside gets frosty, so does the trapped water. Since water increases in volume when it turns to ice, the trapped water expands within the concrete until “spalling” occurs, causing a sidewalk to look like someone has taken a sledgehammer to it. The moisture trapped in the concrete swells until it has no choice but to break out through an unsightly crack of its own creation.
So what's with this Air Entrainment business? The entrainment process scatters millions of micro-bubbles uniformly throughout the concrete matrix via the introduction of surfactants that produce the effect. These ridiculously tiny bubbles are 10 to 500 microns in diameter (a human hair is around 50 microns in diameter), and when properly deployed, comprise about 6% of the host concrete's volume.
The net effect of all those fine bubbles in the concrete? They act as a sort of internal shock absorber. When moisture inevitably does get inside the concrete and attempts to swell into the surrounding space, the concrete’s inner structure is able to flex into the aggregate space created by all the micro bubbles. So, even though concrete looks like a rock-solid enemy of the big toe, it is actually an elastic substance that can flex when climatic conditions require it. Cool, right? How on Earth did anyone figure this out?
In 1938 New York (a place whose harsh winter conditions had been beating up road surfaces since the appearance of the automobile), it was noticed that several stretches of roadway were weathering the extreme freezing conditions with surprising success. What these stretches of highway had in common, it was found, was a particular brand of cement, and it was further discovered that this cement’s manufacturing process used tallow-fired kilns.
Tallow (animal fat) was and is a component of the heat-producing fuel in many manufacturing kilns, but tallow has another interesting characteristic. As was already understood by soap manufacturers––who still use it today for its lathering effect––beef tallow is a natural surfactant; that is, it produces bubbles. As it happened, the accidental introduction of the kiln’s beef tallow residue into the concrete company’s product created in the hardened concrete a finely dispersed bubble structure that inadvertently gave the road surface the needed elasticity to flex with the “freeze-thaw” phenomenon.
Since then, concrete manufacturers have so perfected the Air Entrainment process and so maximized its structural benefits, surfactants are a huge global industry within the construction sector. Concrete and soap. Go figure.
How to Manage Entire Construction Budgets Without the Nightmare.
That master strategist Sun Tzu knew a thing or two about out-thinking the competition. Turns out his focus on strategy over strength can be applied to gaining an edge in the construction industry. ... Read More
If you're a construction worker, you're most likely working physical labor and it can get hot if you're working under the sun. Here's a guide for h... Read More
As an architectural statement, the campus is a monument both to Apple’s corporate success and centrality to the global tech culture. At 176 acres, ... Read More
August 8, 2016
"Some of the cool things that we're doing on job sites today are with Rovers and the alive platform. Alive is that software platform that glues to... Read More
The National Association of Women in Construction has a new executive vice president. This change marks a “brand new day and brand new way” for the... Read More
Every construction business owner can learn a lot from competitors. But merely copying them won't do. You will just always stay one step behind. So... Read More
We've selected eight women from all walks of life to ask them one common question: what advice would you give women who want to enter the construct... Read More